There are many edible water-in-oil emulsions, amongst which are edible spreads, such as margarines. Water-in-oil emulsions have a continuous fat phase and a dispersed aqueous phase.
The fat phase of margarine and similar edible fat continuous spreads is often a mixture of liquid oil (i.e. fat that is liquid at ambient temperature) and fat which is solid at ambient temperatures. The solid fat, also called structuring fat or hardstock fat, serves to structure the fat phase and helps to stabilize the emulsion. The hardstock fat also plays an important role in imparting structural characteristics such as a semi-solid, plastic or spreadable consistency. For a margarine or spread, ideally the hardstock fat has such properties that it melts or dissolves at mouth temperature. Otherwise the product may have a heavy and/or waxy mouth feel. The hardstock fat forms a network throughout the liquid oil providing structure to the water-in-oil emulsion. Aqueous phase droplets are retained within the spaces of the lattice of solid fat crystals. In this way coalescence of the droplets and separation of the heavier aqueous phase from the fat phase is prevented.
The technology of edible water-in-oil emulsions is well established. Generally, edible water-in-oil emulsions like margarines and similar edible fat continuous spreads are prepared according to processes that encompass the following steps:                1. Mixing of the liquid oil, the structuring fat and the aqueous phase at a temperature at which the structuring fat is definitely liquid;        2. cooling of the mixture under high shear to induce crystallization of the structuring fat and to create a water-in-oil emulsion by inversion;        3. formation of a fat crystal network to stabilize the resulting water-in-oil emulsion and give the product some degree of firmness;        4. modification of the crystal network to produce the desired firmness, confer plasticity and reduce the water droplet size.        
These steps are usually conducted in a process that involves apparatus that allow heating, cooling and mechanical working of the ingredients, such as the churn process or the votator process. The churn process and the votator process are described in the Ullmans Encyclopedia, Fifth Edition, Volume A 16, pages 156-158.
The type of fat and the ratio of liquid oil and solid fat are chosen such that after proper processing of the fat blend with an aqueous phase a product with a suitable consistency and mouth-feel is obtained.
Vegetable oils are commonly used to prepare margarine fats. The terms ‘fat’ and ‘oil’ are used interchangeably in this specification. Where applicable the prefix ‘liquid’ or ‘solid’ is added to indicate if the fat or oil is liquid or solid at ambient temperature as understood by the person skilled in the art. Vegetable fats are preferred over animal fats because their unsaturated fat composition enhances the spread's nutritional value. Besides that, vegetable fats are a relatively cheap resource. However, natural, non-processed vegetable fats which have hardstock functionality are rare. Natural fats in the context of this specification are fats which as such are present in their non-genetically modified source organism, particularly in the seeds or fruits of particular plants. For acting as hardstock fat such non-processed vegetable fats usually lack the necessary high content of saturated fatty acids with a chain length of at least 16 carbon atoms. Shea fat, cocoa butter and palm oil are a few examples of fats containing a substantial amount of saturated fatty acid.
Fractionation, hydrogenating and interesterification are well known techniques for turning vegetable oils into suitable hardstock fats. The present trend in food processing, however, is to avoid processing, as much as possible and to opt for natural ingredients and natural processing. Natural processing means that the ingredients have a natural origin and after harvesting have been subjected to no other treatment than a refining and/or purification treatment and to no modification treatment whatsoever.
More natural processing appeals to manufacturers, as it may lower the cost of the production process and the required number of processing steps.
Generally, fats with a high content of HUH triglycerides show good structuring properties. “H” denotes a saturated fatty acid residue containing 16 to 24 carbon atoms, preferably with 16 or 18 carbon atoms, i.e. palmitic acid (C16:0) and stearic acid (C18:0). “U” denotes an unsaturated C18 fatty acid residue, such as oleic acid (C18:1) or linoleic acid (C18:2).
Palm oil, although a relatively cheap resource, needs modification before it is suited for use as hardstock fat. On its own, its structuring functionality is insufficient for the manufacture of good products. The relatively low level of saturated fatty acids (<50 wt. %), their unfavourable distribution over the constituting triglycerides and the relatively high content (>15 wt. %) of polyunsaturated fatty acids make it necessary to subject palm oil to an oil modification treatment. Besides its insufficient structuring ability, palm oil also suffers from the abundant presence of POP and PPO type triglycerides that post-crystallize as undesired fat grains in the final fat spread, where “P” denotes palmitic fatty acid residue and “O” denotes an oleic fatty acid residue.
Cocoa butter, in its unprocessed form, contains a high amount of HUH triglycerides and has been used to structure water-in-oil emulsions, such as margarines. However, use of cocoa butter as hardstock fat for spread preparation entails serious disadvantages. Cocoa butter also suffers, as exampled in its main application, chocolate manufacture, from severe re-crystallisation phenomena, which is known as fat blooming. Similar defects are feared in spread preparation which would easily spoil the product's consistency. Finally, cocoa butter is generally too expensive to serve as hardstock fat in margarine manufacture.
Shea fat, although having a high content of HUH triglycerides, needs to be fractionated before use, because it contains up to 10 wt. % of non-saponifiable matter. The stearin contains 73 wt. % of HUH where nearly all H are stearic acid residues and nearly all U are oleic acid residues. The high costs of fractionation are prohibitive for the commercial use of shea stearin in spread manufacture.
Natural, non-processed hardstock fats with a high content of HUH in which H mainly is a stearic acid residue, are still much sought ingredients for the manufacture of emulsion spreads with a more natural fat phase (i.e. a fat phase comprising a larger part of natural fats).
WO 02/41699 describes Allanblackia fat and Pentadesma fat as vegetable fats which such a beneficial triglyceride composition that they can be used as natural hardstock fat for water-in-oil emulsions. Besides refining, these fats do not need any modification. Allanblackia fat and Pentadesma fat contain a high StOSt triglyceride content: about 65 wt. % of the triglycerides of Allanblackia fat and about 48 wt. % of the triglycerides of Pentadesma fat, where “St” denotes a stearic fatty acid residue.
WO 02/41698 describes an edible W/O emulsion spread which employs Allanblackia and Pentadesma fats as natural hardstock fats. The described composition comprises 70-20 wt. % of an aqueous phase dispersed in 30-80 wt. % of a fat phase which fat phase is a mixture of 50-99 wt. % of a vegetable oil and 1-50 wt. % of a vegetable hardstock fat, characterized in that at least 5 wt. %, preferably at least 50 wt. % of the hardstock fat is either Allanblackia fat or Pentadesma fat or a mixture of both.
WO03/096817 describes how interesterification of natural fats with a relatively high stearic acid residue content with another fat containing a relatively large amount of C12 and C14 fatty acid residues may further improve the structuring properties of such fats.
A recent trend is the development of food products which have a reduced calorie and fat content. As such, low-fat spreads are of interest which may for example function as alternative to higher fat margarines and butters.
The preparation of low fat margarine spreads is well known in the art. Usually, the production process involves the preparation of a water-continuous pre-emulsion which is subsequently made to undergo a phase inversion by means of cooling and working.
A low fat margarine spread comprising a hardstock fat with a large amount HUH, in particular StOSt triglycerides, combines the benefits of both low fat margarines and said triglycerides. Therefore such a spread is highly desirable. However, we have found that upon processing low fat margarine formulations with a large amount of HUH triglycerides, the phase inversion step is often unstable, and leads for instance to loss of the inversion or to water-in-oil emulsions that break upon spreading.